No creature is safe from parasites

September 14, 2012

Article Photos

AP photoThis photo combo shows, from top, a wood tick — or dog tick — clinging to a pencil, in Springfield, Ill.; mosquitoes at the Dallas County mosquito lab; and a rat wandering the subway tracks at Union Square in New York. Hantavirus, West Nile, Lyme disease and now, bubonic plague can be spread potentially by ticks, mosquitoes and rats.

And so, ad infinitum"

- Augustus DeMorgan

That little rhyme was written a long, long time ago, but it is very true.

Someone mentioned seeing a fly sitting on the back of a praying mantis and remarked how strange that seemed. It does seem strange, considering what fierce killers mantises are. However, even the fiercest killers are not safe from parasites.

The simplest definition of a parasite is an organism that lives in or on another organism (host) at the host's expense. I think it is funny that the term "host" is used, as if someone is being invited for dinner, since in this case the host usually is dinner!

There are different types of parasites with different terms used to describe them, but I am simply going to lump them all under parasites.

A true parasite does not kill its host because it needs it to survive. Lice, fleas, tapeworms and bot flies are good examples.

Parasites that do kill their hosts are called parasitoids. Their eggs are laid in or on hosts or in places where their larvae can reach hosts. Their larvae grow inside the host's body, slowly devouring the host's insides and finally killing it. Then they burst out of the host to pupate and become free-living adults.

The commonest examples of parasitoids are the tiny wasps that attack tomato hornworm caterpillars and burst out to spin their little white cocoons on the worm's back. If you have never grown tomatoes, another example is the creature in the "Alien" movies!

Another type of parasite is the nest or egg parasite. The "fly" on the praying mantis was actually a parasitic wasp. The wasp attaches herself to the back of a female mantis (out of reach of the deadly jaws), and rides around until the mantis lays her eggs. Then the wasp gets off and inserts her own eggs into the mantis' egg case. Her larvae will hatch and devour the mantis eggs.

Some insects sneak into the nests of others and lay eggs. Their larvae eat the host's eggs and/or larvae and then eat the provisions the host had stored for its own larvae.

The cuckoo bee does this. She is a bee that looks more like a wasp. She watches solitary bees such as miner and leafcutter bees, and when they fly off to visit flowers, she enters their nests and lays her eggs. Cuckoo wasps have similar habits. They are beautifully colored metallic blue or green and look more like bees than wasps.

The male mud dauber wasp is one of the few male insects that helps the female. While the female is off gathering mud or food, he stays at the nest to chase off parasitic bees, wasps and flies that try to get in. I enjoy watching mud daubers at work, and I always notice the potential nest robbers that come around as soon as the female flies out.

There are many parasites that live inside ant nests. They are usually called "inquilines" which means guests or lodgers, but they are the kind of free-loading guests that nobody wants. Some simply hide and steal food, while others disguise themselves as ants, either by odor or behavior, and "con" the ants into feeding them. Some of them even eat the ants' eggs and brood. They include several species of beetles, crickets, mites, caterpillars and other species of ants.

Parasites are not safe from other parasites. There are tiny parasitoid wasps that attack larger parasitoid wasps.